Digital motion picture decoding apparatus and digital motion picture decoding method

ABSTRACT

A digital motion picture decoding apparatus comprising an input buffer memory for storing coded data to be decoded, a reproduced picture memory for storing the decoded picture data to be displayed, and a display picture deciding means for deciding a reproduced picture to be output from the picture data stored in the reproduced picture memory, further comprises: a program changing means for changing the type of the coded data to be decoded; a program change detecting means for detecting from the output of the program changing means that the type of the coded data to be decoded is changed; and a display state maintaining means for controlling the picture data output from the reproduced picture memory so as to maintain the display state of the reproduced picture which is currently displayed according to the decision of the display picture deciding means, when it is detected from the output of the program change detecting means that the change of the type of the coded data to be decoded makes the coded data not continuous in time sequence.

This application is a continuation of application Ser. No. 10/028,695filed Dec. 28, 2001, now U.S. Pat. No. 6,728,475 which is a continuationof application Ser. No. 08/961,988, filed Oct. 31, 1997 now U.S. Pat.No. 6,393,204.

FIELD OF THE INVENTION

The invention relates to a digital motion picture decoding apparatus anda digital motion picture decoding method for decoding picture data codedby variable length coding for digital storage media, broadcasting, andcommunication. In particular, it relates to a digital motion picturedecoding apparatus and a digital motion picture decoding method capableof correctly decoding and reproducing coded data which is partiallydiscontinuous due to change of program during the reproduction.

BACKGROUND OF THF INVENTION

Nowadays, demands for general method for coding motion picture and itsattached sound are increasing for various applications including digitalstorage media, or television broadcasting and communication. MotionPicture Experts Group (MPEG) in the International ElectrotechnicalCommission (IEC) of International Standardization Organization (ISO) hasproceeded International standardization of motion picture coding methodand already standardized several methods including ISO/IEC 13818-2(MPEG2video).

Here a description is given, with reference to FIG. 9, of a conventionaldigital motion picture decoding apparatus for decoding the data coded bythe MPEG coding method which is disclosed by Japanese Published PatentApplication Number H8-32927, for example.

Reference numeral 900 designates a conventional digital motion picturedecoding apparatus, numeral 911 designates a channel selecting meanswhich takes coded video streams corresponding to plural programs asinputs and, in response to a program select signal input by a user,selects a bit stream corresponding to one of the plural programs tooutput the bit stream as coded picture data 901. This means is alsoconfigured to output a program change signal at the same time. Theoutput coded picture data 901 passes through a code pattern detectingmeans 903 which is described later and is sequentially stored in aninput buffer memory 902.

The code pattern detecting means 903 is a block which inhibits data frompassing through to the input buffer memory 902 until a prescribed codepattern, I picture (intra-coded picture) of GOP (Group of pictures), isdetected based on a change detection signal from the coded data changedetecting means 904, and this means normally allows the data to passthrough during the reproduction processing.

Reference numeral 905 designates a decoding means which makes a requestfor data to the input buffer memory 902, where the data obtained issubjected to decoding processing and then successively stored into apredetermined reproduced picture area in a reproduced picture memory907.

A display picture deciding means 906 decides a reproduced picture to bedisplayed according to time information of each reproduced picture andthe information about the data stored in the reproduced picture memory907 obtained from a time information managing means 908 and a reproducedpicture area managing means 909, outputting the picture as a reproducedpicture data 910 for reproduction and display.

Next, a description is given of the operation for a transition fromnormal reproduction mode to special reproduction mode in whichreproduction speed is changed to realize high-speed reproduction.

In response to a request for high-speed reproduction from a user, thecoded picture data 901 is transmitted to the code pattern detectingmeans 903 in a format which comprises only an intra-frame coded picture(I picture) extracted from the bit stream recorded in record medium, andby detecting a pattern of contiguous I pictures, it is detected that thetransition to special reproduction mode has been completed. Followingthis, sending data through to the input buffer memory 902 is stopped anda clear signal is output from the code pattern detecting means 903 tothe input buffer memory 902, whereby the data stored in the input buffermemory 902 is erased.

When the code pattern detecting means 903 detects normal pattern again,cancel of the special reproduction mode is recognized and a blue-backprocessing which is described later is canceled, whereby sending data tothe input buffer memory 902 is resumed.

Next, a description is given of the operation in the above-describedconfiguration when the coded data in the process of reproduction becomespartially discontinuous due to change of program.

After detecting based on a program change detection signal that changeof the coded data to be input has been performed, the coded data changedetecting means 904 sends a clear signal to the input buffer memory 902to clear all the data stored in the memory 902, while sending a datapassing inhibit signal to the code pattern detecting means 903 in orderto inhibit data from passing through to the input buffer memory 902until a start code (I picture) of an intra-frame coded picture isdetected by the code pattern detecting means 903.

At this time, blank pictures (Bu pictures) are inserted following abidirectional predictive coded picture B3 (B picture), resulting inblue-back processing which provides a screen turned to blue.

Then, when the code pattern detecting means 903 detects the start code(I picture) of the intra-frame coded picture from the coded picture dataafter the change, passing data through to the input buffer memory 902 ispermitted again and the blue-back processing is canceled, wherebyreproduction operation is started again.

The decoding apparatus is configured to prevent reference picture errorcaused by connecting data arrays of different types at the change ofcoded data and avoid decoding the data left in the buffer at the changeof the coded picture data, by performing the above-described processing.

The prior art digital motion picture decoding apparatus and the digitalmotion picture decoding method have the above-described constructionwhich prevents reference picture error caused by connecting differenttypes of data arrays at the change of coded data, but both theconventional decoding apparatus and the method have a problem that whenthe coded data is changed due to the change of program or other causes,blue-back screen is maintained during a prescribed period of time,making a viewer feel unconformable.

Moreover, in the case that change of coded data is not performed on asingle piece of picture data basis and the coded data to be input ischanged in the process of decoding a single piece of picture data bymeans of the decoding means 905, the operation of changing program inthe middle of decoding processing as shown in FIG. 8( a) allows asituation as shown in FIG. 8( b) which is equal to the situation causedby inputting a data array to which a different type of data array isconnected, resulting in decoding error and the considerably confuseddisplay resulted from error picture.

Furthermore, as shown in FIG. 5, since the structure of the data codedby a method employing bidirectional coding such as MPEG coding has anorder different from both the order in which the picture data of thecoded data is placed and the display order for reproducing pictures,forward predictive coded picture (P pictures), which is to be displayedfollowing a sequence of bidirectional predictive coded pictures (Bpictures), is decoded before decoding of the bidirectional predictivecoded pictures (B pictures), and the resultant decoded data is stored inthe reproduced picture memory 907. Therefore, as shown in FIG. 6), inthe configuration only capable of clearing the data in the input buffermemory at the last stage, when the decoding processing has been alreadycompleted at the change of the coded picture data to be input andreproduced picture data which is not displayed yet (P6) is stored in thereproduced picture memory because the display time is not reached, thatreproduced picture data is certainly displayed when the display timebased on time information of the reproduced picture is reached.Therefore, with a long interval between each display time of reproducedpictures, an extended period of time is required before displaying thereproduced picture data which is unnecessary (P6) and it takes much timeto change the coded picture data in the process of reproduction, wherebythe blue-back screen is displayed for an extended period of time andmakes a viewer feel uncomfortable.

SUMMARY OF THE INVENTION

An object of the invention is to provide a digital motion picturedecoding apparatus and a digital motion picture decoding method which donot display blue-back screen during change of coded data due to changeof program or the like, in order to prevent a viewer from feelinguncomfortable.

A further object of the invention is to provide a digital motion picturedecoding apparatus and a digital motion picture decoding method which donot cause decoding error even when coded data is not changed on a singlepiece of picture data basis and the coded data to be input is changedwhen a single piece of picture data is being subjected to decodingprocessing.

A still further object of the invention is to provide a digital motionpicture decoding apparatus and a digital motion picture decoding methodwhich require a short time before displaying the reproduced picture datawhich is unnecessary and do not take much time to change the codedpicture data in the process of reproduction, in the case that one pieceof picture data, whose display time established according to timeinformation on a display picture basis is not reached, has been alreadydecoded at the change of coded picture data, and the reproduced pictureis stored in the reproduced picture memory.

Other objects and advantages of the invention will become apparent fromthe detailed description that follows. The detailed description andspecific embodiments described are provided only for illustration sincevarious additions and modifications within the scope of the inventionwill be apparent to those of skill in the art from the detaileddescription.

According to a first aspect of the present invention, a digital motionpicture decoding apparatus comprising an input buffer memory for storingcoded data to be decoded, a reproduced picture memory for storing thedecoded picture data to be displayed, and a display picture decidingmeans for deciding from the picture data stored in the reproducedpicture memory a reproduced picture to be output, further comprises: aprogram changing means for changing the type of the coded data to bedecoded; a program change detecting means for detecting from the outputof the program changing means that the type of the coded data to bedecoded is changed; and a display state maintaining means forcontrolling the picture data output from the reproduced picture memoryso as to maintain the display state of the reproduced picture beingcurrently displayed according to the decision of the display picturedeciding means, when it is detected from the output of the programchange detecting means that the change of the type of the coded data tobe decoded makes the coded data not continuous in time sequence.

According to a second aspect of the present invention, in the digitalmotion picture decoding apparatus defined in the first aspect, theprogram change detecting means detects from an output of the programchanging means a difference between a normal reproduction state and areproduction state after change of program or a reproduction state at areproduction rate different from the normal reproduction rate.

According to a third aspect of the present invention, the digital motionpicture decoding apparatus defined in the first aspect further comprisesan input buffer memory erasing means for erasing the coded data to bedecoded which is stored therein, when the program change detecting meansdetects that the data subjected to decoding is not continuous in timesequence.

According to a fourth aspect of the present invention, a digital motionpicture decoding apparatus comprising an input buffer memory for storingcoded data to be decoded, a reproduced picture memory for storingdecoded picture data to be displayed, and a display picture decidingmeans for deciding from the picture data stored in the reproducedpicture memory a reproduced picture to be output, further comprises: aprogram changing means for changing the type of the coded data to bedecoded; a program change detecting means for detecting from the outputof the program changing means that the type of the coded data to bedecoded is changed; a reproduced picture memory nullifying means fornullifying the data stored in the reproduced picture memory other thanthe data corresponding to the reproduced picture being currentlydisplayed, when it is detected from the output of the program changedetecting means that the change of the type of the coded data to bedecoded makes the coded data not continuous in time sequence.

According to a fifth aspect of the present invention, the digital motionpicture decoding apparatus defined in the fourth aspect comprises areproduced picture area managing means for managing memory areainformation used when the decoding means writes the decoded picture datainto the reproduced picture memory, and in this apparatus, thereproduced picture memory nullifying means erases the memory areainformation corresponding to the data stored in the reproduced picturearea managing means except the data corresponding to a reproducedpicture being currently displayed.

According to a sixth aspect of the present invention, in the digitalmotion picture decoding apparatus defined in the fourth aspect, thereproduced picture memory nullifying means erases the data in thereproduced picture memory except the data corresponding to thereproduced picture being currently displayed.

According to a seventh aspect of the present invention, in the digitalmotion picture decoding apparatus defined in the fourth aspect, picturedata to be decoded next is written into a nullified memory area of thereproduced picture memory.

According to an eighth aspect of the present invention, a digital motionpicture decoding apparatus comprising an input buffer memory for storingcoded data to be decoded, a reproduced picture memory for storingdecoded picture data to be displayed, and a display picture decidingmeans for deciding from the picture data stored in the reproducedpicture memory a display picture to be output, further comprises: aprogram changing means for changing the type of the coded data to bedecoded; a program change detecting means for detecting from the outputof the program changing means that the type of the coded data to bedecoded is changed; and a decoding stopping means for stopping decodingprocessing by the decoding means and controlling the decoding means suchthat the data being in the process of decoding at that time is writteninto the reproduced picture memory as the already decoded one, when itis detected from the output of the program change detecting means thatthe change of the type of the coded data to be decoded makes the codeddata not continuous in time sequence.

According to a ninth aspect of the present invention, a digital motionpicture decoding method comprises the steps of: detecting whether datais continuous in time sequence during decoding processing; andmaintaining the display state of a reproduced picture being currentlydisplayed when it is found in the first step that the data is notcontinuous in time sequence during the decoding processing.

According to a tenth aspect of the present invention, a digital motionpicture decoding method comprises the steps of: detecting whether datais continuous in time sequence during decoding processing; andnullifying data other than the one corresponding to a reproduced picturebeing currently displayed, when it is judged in the first step that thedata is not continuous in time sequence during the decoding processing.

According to an eleventh aspect of the present invention, the digitalmotion picture decoding method defined in the tenth aspect furthercomprises a step of stopping decoding processing and processing the databeing currently decoded at that time as the already decoded one, when itis judged in the first step that the data is not continuous in timesequence during the decoding processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a digital motion picture decoding apparatusaccording to an embodiment of the present invention.

FIG. 2 is a flow chart for explaining the operation during change ofprogram by the digital motion picture decoding apparatus of theembodiment of the invention.

FIG. 3 is a flow chart for explaining the operation of the decodingmeans during change of program in the digital motion picture decodingapparatus of the embodiment of the invention.

FIG. 4 is a flow chart for explaining the operation for displaying newcoded data after change of program in the digital motion picturedecoding apparatus of the embodiment of the invention.

FIG. 5 is a diagram showing an example of the structure of a bit streamcoded in a coding mode which uses a bidirectional predictive coding suchas MPEG.

FIG. 6 is a diagram showing an example of the structure of a bit streamand an exemplary operation of the conventional digital motion picturedecoding apparatus, in the case that coded data to be input is changedin the process of reproduction.

FIG. 7 is a diagram illustrating an exemplary operation of a digitalmotion picture decoding apparatus of the present invention under thecondition illustrated in FIG. 5.

FIGS. 8( a) to 8(c) are diagrams showing the states of a decoding meansin the case that coded data is changed in the middle of decoding onepiece of picture data.

FIG. 9 is a block diagram of a prior art digital motion picture decodingapparatus.

FIG. 10 is a conceptual diagram of a state table of reproduced pictureareas which constitute the digital motion picture decoding apparatusaccording to the embodiment of the present invention.

PREFERRED EMBODIMENT OF THE INVENTION

Hereinafter a description is given of a digital motion picture decodingapparatus and a digital motion picture decoding method according to thepresent invention with reference to drawings.

FIG. 1 is a block diagram of a digital motion picture decoding apparatusaccording to an embodiment of the invention. In the figure, referencenumeral 100 designates a digital motion picture decoding apparatus ofthe invention, and numeral 104 designates a program change detectingmeans, which means takes coded video streams corresponding to aplurality of coded programs as inputs and, according to a program selectsignal input by a user through a control means (remote controller) 111,selects one bit stream corresponding to one of the plural programs tooutput it as coded picture data 101.

In normal decoding operation, the input coded picture data 101 is passedthrough a code pattern detecting means 103 which is described later, andstored in an input buffer memory 102.

The input buffer memory 102 has a relatively large capacity, forexample, about 400 Kb, and outputs the stored coded data according to arequest from a decoding means 105 which is also described later.

The decoding means 105 manages an amount of data in the input buffermemory 102 based on the amount of the data input into this means and theamount of the data output from the means, and controls the data input tothe means itself according to the amount of the data stored in the inputbuffer memory 102. Moreover, the decoding means 105 also includes areproduced picture memory address management table for managing nulladdresses when the decoded picture data is written into a reproducedpicture memory 107 which is also described later.

The code pattern detecting means 103 is a block which inhibits data frompassing through to the input buffer memory 102 until a predeterminedcode pattern is detected, according to a data passing inhibit signalfrom the program change detecting means 104, and this means normallyallows data to passing through during reproduction.

The reproduced picture memory 107, which comprises SDRAM, for example,has a capacity for storing three frames of picture data (500 Kb×3=1.5Mb) and includes divided regions M0 to M2. The coded picture data inputto the decoding means 105 to be decoded is stored into one of thereproduced picture regions M0 to M3 in the reproduced picture memory107, on one display picture basis.

The display picture deciding means 106 comprises a base time counter forcounting up with time precision equal or superior to the time precisionof the time information established on single frame picture basis by atime information managing means 108 which is described later, and thisbase time counter manages a base time for reproduction operation.Moreover, the base time counter can change its count according to thebase time information signal input from the decoding means 105. Then,when it is judged from a comparison between the count of the base timecounter and a value of the time information from the reproduced picturearea managing means 109 which is described later that these values areequal or approximately equal, this means decides a reproduced picturearea as an output area according to the data storage information fromthe reproduced picture area managing means 109. Then, to output thedecoded data in this area, the deciding means outputs a signal forselecting a reproduced picture area from which decoded data is to beoutput (this signal is hereinafter referred to as an outputarea-reproduced picture area select signal), to the reproduced picturememory 107 and the reproduced picture area managing means 109.

Reference numeral 109 designates the reproduced picture area managingmeans, and this managing means relates the information indicating whichreproduced picture area of the reproduced picture memory 107 stores thedecoded picture data, to a display state flag fed back from the displaypicture deciding means 106 which is described later, and performsmanagement using a table as shown in FIG. 10, for example.

Further in the above configuration, the control means (remotecontroller) 111 implements a program changing means, and the programchange detecting means 104 implements a program change detecting meansfor detecting change of program according to a program select signalinput from the control means (remote controller) 111, and an inputbuffer memory erasing means for erasing the data stored in the inputbuffer memory 102. The display picture deciding means 106 and thereproduced picture area managing means 109 implement a display statemaintaining means and the program change detecting means 104 and thereproduced picture area managing means 109 implement a reproducedpicture memory nullifying means and a decoding stopping means.

FIGS. 2 and 4 are flow charts illustrating the processes performed bythe digital motion picture decoding apparatus, and the operation will bedescribed with reference to these flow charts.

Before the description, it is assumed that among the picture data storedin the reproduced picture memory 107, a piece of picture data stored inreproduced picture area M1 is currently reproduced corresponding to aspecified program selected by user input.

Next, a description is given of the operation performed in the case thatdata array subjected to decoding processing becomes non-continuous atsome midpoint because coded data is changed during the reproduction,with reference to the block diagram of FIG. 1 and the flow chart of FIG.2.

Program change processing in the middle of reproduction starts asfollows; in step S1, the control means (remote controller) 111 changes aprogram desired to be reproduced in the process of reproduction andoutputs to the program change detecting means 104 a program selectsignal for changing coded data to be reproduced.

Then, in step S2, the program change detecting means 104 outputs to thecode pattern detecting means 103 a data passing inhibit signal forinhibiting coded data from passing through until a prescribed code isdetected, and simultaneously outputs to the input buffer memory 102 adata clear signal for clearing all the data currently stored in thismemory 102. Further, at the same time, this means also outputs to thedecoding means 105 a decoding stop signal for stopping the currentlyperformed decoding, and to the reproduced picture area managing means109, a flag erase signal for clearing the data in the areas other thanthe area for a reproduced picture being currently displayed.

Thereafter, the program change detecting means 104 selects coded data ofa program, from the stream data arrays of plural programs which havebeen input, according to the program select signal from the controlmeans (remote controller) 111, and starts outputting the coded data tothe code pattern detecting means 103.

In response to the input of the data passing inhibit signal, the codepattern detecting means 103 inhibits the input coded data from passingthrough to the input buffer memory 102 and waits for the input of asequence header code of the coded data based on MPEG.

Further, the input buffer memory 102 clears all the stored data inresponse to the input data clear signal and waits the data input fromthe code pattern detecting means 103.

Furthermore, the decoding means 105 stops the currently performeddecoding processing in response to the input of the decoding stoppingsignal and waits for the input of a sequence header code. Thereafter,this means outputs a data request signal requesting new coded data tothe input buffer memory 102.

In step S3, when data is input, it is checked whether the data is asequence header code or not. The data which is not the sequence headercode is discarded, and a check is made for next input data to seewhether the data is a sequence header code or not. The process in stepS3 is repeated until a sequence header code is input.

As described above, in the digital motion picture decoding apparatus ofthe conventional configuration, by stopping the decoding processingimmediately after change of program, a state is brought about which isequal to the state that different types of data arrays connected to eachother are input to the decoding means. This results in decoding error,and considerably confused display caused by displaying error pictures,which makes viewer feel uncomfortable.

Further, the reproduced picture area managing means 109 clears the datain the reproduced picture memory 107 except the data in the area for thereproduced picture being currently used as a display output, by means ofa flag erase signal. More specifically, flags are changed so that thedata storage information about the reproduced picture memory 107indicates-“no data” except the one-about-the reproduced picture area M1.This process resolves one of the problems occurred in the digital motionpicture decoding apparatus of the conventional configuration thatdisplaying unnecessary reproduced picture data prolongs a time intervalbetween change of the coded picture data to be input and change ofreproduced pictures.

Furthermore, data storage information and a time information notifyingsignal are output to the display picture deciding means 106, theinformation and the signal both being the contents of the reproducedpicture area state table changed to the state after data clearimmediately after clearing the data in the reproduced picture memory107.

According to the data storage information and the time informationnotifying signal from the reproduced picture area managing means 109,the display picture deciding means 106 detects that there is no data inreproduced picture areas except the one being currently used as anoutput area for display, and outputs to the reproduced picture memory107 an output area-reproduced picture select signal which instructs tooutput the data from this reproduced picture area repeatedly because thereproduced picture areas other than that area contains no data. Thisprocess resolves one of the problems for the digital motion picturedecoding apparatus of the conventional configuration that blue-backdisplay processing (see Bu in FIG. 6) performed until the display of anew picture after the change (see IO′ in FIG. 6) causes a display statetransition which is considerably clumsy.

Next, a description is given of the operation in the process ofdisplaying new coded data obtained after change of program.

In step S3, the code pattern detecting means 103 analyzes new coded dataobtained from the program change detecting means 104 to detect asequence header code and, when the sequence head code is detected, thestep is followed by step S4 in which passing coded data through to theinput buffer memory 102 is permitted again.

This step is followed by step S5, in which storing coded data into theinput buffer memory 102 is resumed with the data following the sequenceheader code being initial one, and outputting the data is startedcorresponding to the data request signal from the decoding means 105.

In step S6, from the coded data which includes display order informationfor single frame picture being currently decoded and the timeinformation about the times at which the picture should be displayed,the decoding means 105 extracts the above information to output it as anextracted information signal to the time information managing means 108.If the coded data contains no time information based on which a singleframe pictures being currently decoded is displayed, the display orderinformation only is output to the time information managing means 108 asan extracted information signal. Moreover, the decoding means 105extracts the base time information contained in the coded data andoutputs it as a base time information signal to the display picturedeciding means 106.

Following this, the same operation as in normal reproduction isperformed: as shown in the flow chart of FIG. 3, in step S7, thedecoding means 105 judges whether the input coded data is predictivecoded data or not; when the coded data is a predictive coded one, thisstep is followed by step S8 wherein a reference picture data requestsignal is output to the reproduced picture area managing means 109 torequest necessary data. If the input coded data is not a predictivecoded one, decoding processing is performed using the input coded dataonly.

Then, in step S9, the reproduced picture area managing means 109 checkswhich reproduced picture area of the reproduced picture memory 107stores the requested reference picture data, and in step S10, thereproduced picture area managing means 109 outputs a reference picturedata output control signal which instructs to output the data in thespecified area as reference picture data.

In step S11, the reproduced picture memory 107 outputs the data in thespecified area as reference picture data, according to the instructionof the reference picture data output control signal.

Then, in step S12, the decoding means 105 starts decoding the predictivecoding type coded data using the input reference picture data.

In step S12-1, the decoding means 105 outputs decoded data obtained bythe decoding processing to the reproduced picture memory 107. Thereproduced picture area managing means 109 outputs to the reproducedpicture memory 107 an address signal which instructs the area in whichthat decoded data is to be stored.

If the coded data in the process of decoding contains base timeinformation, the information is output to the display picture decidingmeans 106 as base time information.

Further, the display order information for displaying a single framepicture being in the process of decoding and the time information basedon which such picture is displayed are extracted from the coded data andoutput as an extracted information signal to the time informationmanaging means 108. If the above-described time information is notincluded in the coded data, the display order information only isextracted and output as an extracted information signal to the timeinformation managing means 108.

Next, the time information managing means 108 judges whether the timeinformation extracted from the coded data is included in an extractedinformation signal which is input, and when the time information isincluded, this time information is determined as the time informationbased on which the picture is to be displayed, which picture iscurrently being decoded in the decoding means 105, and output as a timeinformation signal to the reproduced picture area managing means 109. Ifthe time information is not found, time information based on which thesingle frame picture being currently decoded is to be displayed iscalculated from time information and display order information foranother single frame picture, both previously input from the decodingmeans 105, and the display order information for the single framepicture being currently decoded, outputting it as a time informationsignal to the reproduced picture area managing means 109.

Next, in step S16, the reproduced picture area managing means 109 checksthe contents of the reproduced picture area state table, outputting newdecoded data obtained from the decoding means 105 after the change ofprogram to the reproduced picture areas other than the reproducedpicture area from which the display is being output (M1), that is, M0and M2, and from these areas the decoded data has been cleared. Thereproduced picture area managing means 109 also changes the contents ofthe reproduced picture area state table, outputting data storageinformation and a time information notifying signal to the displaypicture deciding means 106.

Then, in step S17, the display picture deciding means 106 detects fromthe data storage information and the time information notifying signalthe fact that new picture is ready to be output, outputting an outputarea-reproduced picture area select signal such that the decoded data ofthe picture stored in one of the reproduced picture areas will be outputwhen the time based on the time information for the picture is reached.

Following this step, in step S18, the reproduced picture memory 107outputs new decoded data obtained after the change of program asreproduced picture data, according to the output area-reproduced picturearea select signal.

The above-described processes enable to change a picture to bedisplayed, according to the content of a newly selected program.

As described above, in the first embodiment, passing data through to theinput buffer memory 102 is inhibited when change of program is detected,and simultaneously all the data in the input buffer memory 102 is erasedwhile the display picture deciding means 106 is controlled to maintainthe display picture at this time. This disables an unnatural screen suchas a blue-back screen to be displayed for a certain period of timeduring the change of program, reducing viewer's uncomfortableness.

Further, when the change of program is detected, the information aboutthe areas in the reproduced picture memory 107 other than that currentlyused as an output area for display is cleared to treat them as nullareas, whereby the display of the unnecessary picture is prevented whichwill be displayed after the change of coded data. Further, since thecoded data obtained after the change is written into the reproducedpicture memory 107 more swiftly, it is possible to reduce a timenecessary to perform the process until the reproduced picture of thecoded data after the change is displayed.

In addition, since the decoding processing performed by the decodingmeans 105 is stopped and a code indicating that decoding a single pieceof picture data is completed is added to the picture data beingcurrently decoded, the data array of a different program is confusedwith the continuous data array being in the process of decoding, therebypreventing the occurrence of decoding error due to this misconceptionand the resultant display of error pictures.

Although in the first embodiment the code pattern detecting means 103and the decoding means 105 have a feature of waiting for a sequenceheader code to be detected after the change of program, any detectionfeature is applicable as long as it can detect a code pattern indicatinga head of a data unit for decoding processing and this detecting targetis not limited to a sequence header code. Other code patterns such as anMPEG-based GOP header code and a start code of an intra-frame codedpicture (I picture) can be used as long as those codes are code patternswhich allow to reproduce picture only from the coded data following thedetected data only.

Although this embodiment is configured such that the code patterndetecting means 103 is placed as a stage followed by the input buffermemory, the same operation can be obtained by the followingconfiguration that the code pattern detecting means 103 is placed as astage following the input buffer memory 102, and the buffer memory 102outputs data according to the request for data from the code patterndetecting means 103 and inhibits the data to be sent to the subsequentdecoding means 105 until the detecting means 103 detects a predeterminedcode pattern.

Although in this embodiment it is assumed that the reproduced picturememory 107 has three reproduced picture areas, the number of thereproduced picture areas is not limited to three and any number ofreproduced picture areas are applicable as long as the number allows thedecoded reproduced picture data to be displayed in a display order.

In addition, although in this embodiment the reproduced picture areas inthe reproduced picture memory 107 are illustrated as contiguous areas,the structure of the reproduced picture memory 107 is not limited tothis illustration and a reproduced picture memory can be employed whichdivides decoded data of each single picture data into non-contiguousareas for storage.

Although in this embodiment a decoding object is MPEG-based coded data,the coded data as a decoding object is not limited to this data codedbased on MPEG, and any coded data is applicable as long as this code isthe one coded by bidirectional predictive coding and therefore the datacoded by any coding method other than MPEG-based coding may be used.

The stream data input to the program change detecting means 104 is notnecessary to be broadcasted and such configuration is applicable inwhich required program stream data is read from record media such asdisks.

Although in this embodiment the count of the base time counter ischanged according to base time information whenever that base timeinformation is input to the display picture deciding means 106, thischange may be performed only when the base time informationcorresponding to the initial part of each coded data to be reproduced isinput to the display picture deciding means 106, or this change may beperformed at arbitrary timing corresponding to the input of a controlsignal from external unit.

Furthermore, in this embodiment, it is not necessary for the base timeinformation to be changed according to the data extracted from the codeddata by the decoding means 105 and external unit may directly set thecount of the base time counter to an arbitrary value.

1. A digital motion picture decoding method comprising the steps of:decoding a coded data as a reproduction picture; outputting thereproduction picture; receiving a manually inputted signal which causesonly one discontinuity in time sequence of the coded data to be decodedand which causes decoding of coded data read after the discontinuitylapses as a new reproduction picture; outputting a reproduction picturerepeatedly until the new reproduction picture is ready to be output,after receiving the manually inputted signal; and nullifying decodeddata, including decoded data which has not been outputted, correspondingto coded data read prior to the occurrence of the discontinuity, afterreceiving the manually inputted signal.
 2. The digital motion picturedecoding method of claim 1, wherein the coded data includes predictivecoded data.
 3. The digital motion picture decoding method of claim 2,wherein the nullifying step further nullifies decoded data other thandecoded data corresponding to the reproduction picture.
 4. The digitalmotion picture decoding method of claim 3, further comprising the stepsof: decoding coded data read after the discontinuity lapses as the newreproduction picture; and outputting the new reproduction picture. 5.The digital motion picture decoding method of claim 4, furthercomprising the steps of: stopping the decoding of coded data read priorto the occurrence of the discontinuity; and nullifying coded data readprior to the occurrence of the discontinuity.
 6. The digital motionpicture decoding method of claim 5, wherein the coded data includesbidirectional predictive coded data.
 7. The digital motion picturedecoding method of claim 6, wherein the coded data is coded by an MPEGcoding method.
 8. The digital motion picture decoding method of claim 7,wherein said MPEG coding method is MPEG 2 coding method.
 9. The digitalmotion picture decoding method of claim 8, wherein the manually inputtedsignal is received from a remote control.
 10. The digital motion picturedecoding method of claim 5, wherein the nullified decoded data is notreproduced thereafter.
 11. A digital motion picture outputting methodcomprising the steps of: outputting a reproduction picture; receiving amanually inputted signal which causes only one discontinuity in timesequence of coded data to be decoded and which causes decoding codeddata read after the discontinuity lapses as a new reproduction picture;outputting a reproduction picture repeatedly until the new reproductionpicture is ready for output, after receiving the manually inputtedsignal; and nullifying decoded data, including decoded data which hasnot been outputted, corresponding to coded data read prior to theoccurrence of the discontinuity, after receiving the manually inputtedsignal.
 12. The digital motion picture outputting method of claim 11,wherein the coded data includes predictive coded data.
 13. The digitalmotion picture outputting method of claim 12, wherein the nullifyingstep further nullifies decoded data other than decoded datacorresponding to the reproduction picture before outputting the newreproduction picture.
 14. The digital motion picture outputting methodof claim 13, further comprising the step of outputting the newreproduction picture.
 15. The digital motion picture outputting methodof claim 14, further comprising the steps of: stopping the decoding ofcoded data read prior to the occurrence of the discontinuity; andnullifying coded data read prior to the occurrence of timediscontinuity.
 16. The digital motion picture outputting method of claim15, wherein the coded data includes bidirectional predictive coded data.17. The digital motion picture outputting method of claim 16, whereinthe coded data is coded by an MPEG coding method.
 18. The digital motionpicture outputting method of claim 17, wherein said MPEG coding methodis MPEG 2 coding method.
 19. The digital motion picture outputtingmethod of claim 18, wherein the manually inputted signal is receivedfrom a remote control.
 20. The digital motion picture outputting methodof claim 15, wherein the nullifying decoded data is not reproducedthereafter.
 21. A digital motion picture decoding apparatus, comprising:a decoder configured to decode coded data as a reproduction picture; anoutputting unit configured to output the reproduction picture; and acontroller configured to receive a manually inputted signal which causesonly one discontinuity in time sequence of a coded data to be decodedand which causes decoding of coded data read after the discontinuitylapses as a new reproduction picture, wherein the controller isconfigured to nullify decoded data, including decoded data which has notbeen outputted, corresponding to coded data read prior to the occurrenceof the discontinuity and is configured to output a reproduction picturerepeatedly until the new reproduction picture is ready to be output,after receiving the manually inputted signal.
 22. The digital motionpicture decoding apparatus of claim 21, wherein the coded data includespredictive coded data.
 23. The digital motion picture decoding apparatusof claim 22, wherein the controller is further configured to nullifydecoded data corresponding to the reproduction picture.
 24. The digitalmotion picture decoding apparatus of claim 23, wherein the outputtingunit outputs the new reproduction picture.
 25. The digital motionpicture decoding apparatus of claim 24, wherein the controller isconfigured to: stop the decoding coded data read prior to the occurrenceof the discontinuity; and nullify coded data read prior to theoccurrence of time discontinuity.
 26. The digital motion picturedecoding apparatus of claim 25, wherein the coded data includesbidirectional predictive coded data.
 27. The digital motion picturedecoding apparatus of claim 26, wherein the coded data is coded by anMPEG coding method.
 28. The digital motion picture decoding apparatus ofclaim 27, wherein said MPEG coding method is MPEG 2 coding method. 29.The digital motion picture decoding apparatus of claim 28, wherein themanually inputted signal is received from a remote control.
 30. Thedigital motion picture decoding apparatus of claim 25, wherein thenullifying decoded data is not reproduced thereafter.
 31. A digitalmotion picture outputting apparatus, comprising: an outputting unitconfigured to output the reproduction picture; and a controllerconfigured to receive a manually inputted signal which causes only onediscontinuity in time sequence of coded data to be decoded and whichcauses decoding of coded data read after the discontinuity lapses as anew reproduction picture, wherein the controller is configured tonullify decoded data, including decoded data which has not beenoutputted, corresponding to coded data read prior to the occurrence ofthe discontinuity and is configured to output a reproduction picturerepeatedly until the new reproduction picture is ready to be displayed,after receiving the manually inputted signal.
 32. The digital motionpicture outputting apparatus of claim 31, wherein the coded dataincludes predictive coded data.
 33. The digital motion pictureoutputting apparatus of claim 32, wherein the controller is furtherconfigured to nullify decoded data corresponding to the reproductionpicture.
 34. The digital motion picture outputting apparatus of claim33, wherein the outputting unit outputs the new reproduction picture.35. The digital motion picture outputting apparatus of claim 34, whereinthe controller is configured to: stop the decoding coded data read priorto the occurrence of the discontinuity; and nullify coded data readprior to the occurrence of time discontinuity.
 36. The digital motionpicture outputting apparatus of claim 35, wherein the coded dataincludes bidirectional predictive coded data.
 37. The digital motionpicture outputting apparatus of claim 36, wherein the coded data iscoded by an MPEG coding method.
 38. The digital motion pictureoutputting apparatus of claim 37, wherein said MPEG coding method isMPEG 2 coding method.
 39. The digital motion picture outputtingapparatus of claim 38, wherein the manually inputted signal is receivedfrom a remote control.
 40. The digital motion picture outputtingapparatus of claim 35, wherein the nullified decoded data is notreproduced thereafter.
 41. A digital motion picture decoding methodcomprising the steps of: decoding coded data as a reproduction picture;outputting the reproduction picture; receiving a manually inputtedsignal; nullifying decoded data which has not been outputted,corresponding to coded data which has been read, in response to themanually inputted signal; and outputting a reproduction picturerepeatedly until the new reproduction picture from coded data read afterreceiving the manually inputted signal is ready to be displayed.
 42. Thedigital motion picture decoding method of claim 41, wherein the codeddata includes predictive coded data.
 43. The digital motion picturedecoding method of claim 42, wherein the nullifying step furthernullifies decoded data other than decoded data corresponding to thereproduction picture before outputting the new reproduction picture. 44.The digital motion picture decoding method of claim 43, furthercomprising the step of: decoding coded data read after receiving themanually inputted signal as the new reproduction picture; and outputtingthe new reproduction picture.
 45. The digital motion picture decodingmethod of claim 44, further comprising the steps of: stopping decodingcoded data which has been read; and nullifying coded data which has beenread.
 46. The digital motion picture decoding method of claim 45,wherein the coded data includes bidirectional predictive coded data. 47.The digital motion picture decoding method of claim 46, wherein thecoded data is coded by an MPEG coding method.
 48. The digital motionpicture decoding method of claim 47, wherein said MPEG coding method isMPEG 2 coding method.
 49. The digital motion picture decoding method ofclaim 48, wherein the manually inputted signal is received from a remotecontrol.
 50. The digital motion picture decoding method of claim 45,wherein the nullifying decoded data is not reproduced thereafter.
 51. Adigital motion picture outputting method comprising the steps of:outputting a reproduction picture; receiving a manually inputted signal;nullifying decoded data which has not been outputted, corresponding tocoded data which has been read, in response to the manually inputtedsignal; and outputting a reproduction picture repeatedly until the newreproduction picture from coded data read after receiving the manuallyinputted signal is ready to be displayed.
 52. The digital motion pictureoutputting method of claim 51, wherein the coded data includespredictive coded data.
 53. The digital motion picture outputting methodof claim 52, wherein the nullifying step further nullifies decoded dataother than decoded data corresponding to the reproduction picture beforeoutputting the new reproduction picture.
 54. The digital motion pictureoutputting method of claim 53, further comprising the step of outputtingthe new reproduction picture.
 55. The digital motion picture outputtingmethod of claim 54, further comprising the steps of: stopping thedecoding of coded data which has been read; and nullifying the codeddata which has been read.
 56. The digital motion picture outputtingmethod of claim 55, wherein the coded data includes bidirectionalpredictive coded data.
 57. The digital motion picture outputting methodof claim 56, wherein the coded data are coded by an MPEG coding method.58. The digital motion picture outputting method of claim 57, whereinsaid MPEG coding method is MPEG 2 coding method.
 59. The digital motionpicture outputting method of claim 58, wherein the manually inputtedsignal is received from a remote control.
 60. The digital motion pictureoutputting method of claim 55, wherein the nullifying decoded datais/are not reproduced thereafter.
 61. A digital motion picture decodingapparatus, comprising: a decoder configured to decode coded data as areproduction picture; an outputting unit configured to output thereproduction picture; and a controller configured to receive a manuallyinputted signal, wherein the controller is configured to: nullifydecoded data which has not been outputted, corresponding to coded datawhich has been read, in response to the manually inputted signal, andoutput a reproduction picture repeatedly until the new reproductionpicture from coded data read after receiving the manually inputtedsignal is ready for display.
 62. The digital motion picture decodingapparatus of claim 61, wherein the coded data includes predictive codeddata.
 63. The digital motion picture decoding apparatus of claim 62,wherein the controller is further configured to nullify decoded dataother than decoded data corresponding to the reproduction picture beforeoutputting the new reproduction picture.
 64. The digital motion picturedecoding apparatus of claim 63, wherein, the decoder decodes coded dataread after receiving the manually inputted signal as the newreproduction picture; and the outputting unit outputs the newreproduction picture.
 65. The digital motion picture decoding apparatusof claim 64, wherein the controller is configured to: stop decoding thecoded data; and nullify coded data which has been read.
 66. The digitalmotion picture decoding apparatus of claim 65, wherein the coded dataincludes bidirectional predictive coded data.
 67. The digital motionpicture decoding apparatus of claim 66, wherein the coded data is codedby an MPEG coding method.
 68. The digital motion picture decodingapparatus of claim 67, wherein said MPEG coding method is MPEG 2 codingmethod.
 69. The digital motion picture decoding apparatus of claim 68,wherein the manually inputted signal is received from a remote control.70. The digital motion picture decoding apparatus of claim 65, whereinthe nullifying decoded data is/are not reproduced thereafter.
 71. Adigital motion picture outputting apparatus, comprising: an outputtingunit configured to output die reproduction picture; and a controllerconfigured to receive a manually inputted signal, wherein the controlleris configured to: nullify decoded data which has not been outputted,corresponding to coded data which has been read, in response to themanually inputted signal; and output a reproduction picture repeatedlyuntil the new reproduction picture from coded data read after receivingthe manually inputted signal is ready to be output.
 72. The digitalmotion picture outputting apparatus of claim 71, wherein the coded dataincludes predictive coded data.
 73. The digital motion pictureoutputting apparatus of claim 72, wherein the controller is furtherconfigured to nullify decoded data other than decoded data correspondingto the reproduction picture before outputting the new reproductionpicture.
 74. The digital motion picture outputting apparatus of claim73, wherein the outputting unit outputs the new reproduction picture.75. The digital motion picture outputting apparatus of claim 74, whereinthe controller is configured to: stop the decoding the coded data; andnullify coded data read prior to receiving the manually inputted signal.76. The digital motion picture outputting apparatus of claim 75, whereinthe coded data includes bidirectional predictive coded data.
 77. Thedigital motion picture outputting apparatus of claim 76, wherein thecoded data is coded by an MPEG coding method.
 78. The digital motionpicture outputting apparatus of claim 77, wherein said MPEG codingmethod is MPEG 2 coding method.
 79. The digital motion pictureoutputting apparatus of claim 78, wherein the manually inputted signalis received from a remote control.
 80. The digital motion pictureoutputting apparatus of claim 75, wherein the nullifying decoded datais/are not reproduced thereafter.
 81. A digital motion picture decodingmethod comprising the steps of: (a) decoding a coded data stream as areproduction picture; (b) receiving a manually inputted signal whichcauses only one discontinuity in time sequence of a coded data stream tobe decoded; (c) maintaining a displayed frame until a frame from codeddata read after the discontinuity lapses is decoded and ready to bedisplayed; and (d) nullifying decoded data, including decoded data whichhas not been displayed and has been decoded before decoding of a framethat has been outputted to be displayed, corresponding to coded dataread prior to the occurrence of the discontinuity.
 82. The digitalmotion picture decoding method according to claim 81, wherein the framethat has been outputted to be displayed corresponds to a displayedframe.
 83. The digital motion picture decoding method according to claim81, wherein the frame that has been outputted to be displayedcorresponds to a frame designated to display next to a displayed frame.84. The method for decoding the motion picture according to claim 81,wherein the coded data stream comprises a plurality of contiguous codedframes.
 85. The method for decoding the digital motion picture accordingto claim 81, further comprising the steps of: (i) identifying from thecoded data stream a frame of a first type; (ii) outputting the frame ofthe first type first from the coded data stream; (iii) identifying fromthe coded data stream a frame of a second type that is before a lastframe in the coded data stream; and (iv) outputting the frame of thesecond type last from the coded data stream.
 86. The method for decodingthe digital motion picture according to claim 85, wherein the frame ofthe first type corresponds to an intra-frame coded picture.
 87. Themethod for decoding the digital motion picture according to claim 85,wherein the frame of the second type corresponds to a forward predictivecoded picture.
 88. The method for decoding the digital motion pictureaccording to claim 85, further comprising the steps of: (v) identifyingfrom the coded data stream a frame of a third type after the frame ofthe second type; and (vi) outputting the frame of the third type afterthe frame of the first type and before the frame of the second type. 89.The method for decoding the digital motion picture according to claim88, wherein the frame of the third type corresponds to a bidirectionalpredictive coded picture.
 90. The method for decoding the digital motionpicture according to claim 81, further comprising the steps of: (i)storing a plurality of frames decoded from the coded data stream; and(ii) selecting a stored frame to be output.
 91. The method for decodingthe digital motion picture according to claim 90, wherein step (c)further comprises the step of reselecting the stored frame to beoutputted until the frame from coded data read after the discontinuitylapses is decoded and ready to be displayed.
 92. The method for decodingthe digital motion picture according to claim 91, wherein the frame tobe reselected corresponds to the frame outputted upon receiving theinterrupt signal.
 93. The method for decoding the digital motion pictureaccording to claim 81, wherein the coded data coded by an MPEG codingscheme.
 94. The method for decoding the digital motion picture accordingto claim 93, wherein said MPEG coding scheme is MPEG 2 coding scheme.95. The method for decoding the digital motion picture according toclaim 94, wherein the manually inputted signal is received from anexternal device.
 96. A method of reproducing a digital motion picturecomprising a first series of coded frames arranged in a first order anda second series of coded frames, comprising the steps of: (a) decodingthe first series of coded frames in the first order; (b) outputtingframes decoded in step (a) in a second order different from the firstorder; (c) receiving an interrupt signal when at least one frame hasbeen outputted in step (b); (d) decoding the second series of codedframes further to the interrupt signal; (e) nullifying at least oneframe that has been decoded in step (a) but has not been outputtedaccording to the second order; and (f) maintaining a frame that has beenoutputted according to the second order at least until a frame of thesecond series has been decoded and is ready to be outputted.
 97. Themethod for decoding the motion picture according to claim 96, whereinthe first series and the second series each comprise a plurality ofcontiguous frames.
 98. The method for decoding the motion pictureaccording to claim 96, wherein in step (b) the frames are outputted tobe displayed.
 99. The method for decoding the digital motion pictureaccording to claim 96, wherein execution of steps (a) and (b) at leastpartially overlap.
 100. The method for decoding the digital motionpicture according to claim 96, wherein step (f) further comprises thestep of repeatedly outputting the frame that has been outputtedaccording to the second order at least until the frame of the secondseries has been decoded and is ready to be outputted.
 101. The methodfor decoding the digital motion picture according to claim 96, furthercomprising the steps of: (i)identifying from the first series a frame ofa first type; (ii)outputting the frame of the first type first from theseries; (iii) identifying from the first series a frame of a second typetat is before a last frame in the first series; and (iv) outputting theframe of the second type last from the first series.
 102. The method fordecoding the digital motion picture according to claim 101, wherein theframe of the first type corresponds to an intra-frame coded picture.103. The method for decoding the digital motion picture according toclaim 101, wherein the frame of the second type corresponds to a forwardpredictive coded picture.
 104. The method for decoding the digitalmotion picture according to claim 101, further comprising the steps of:(v) identifying from the first series a frame of a third type after theframe of the second type; and (vi) outputting the frame of the thirdtype after the frame of the first type and before the frame of thesecond type.
 105. The method for decoding the digital motion pictureaccording to claim 104, wherein the frame of the third type correspondsto a bidirectional predictive coded picture.
 106. The method fordecoding the digital motion picture according to claim 96, furthercomprising the steps of: (v) storing the frames decoded in step (a); and(vi) selecting a stored frame to be output according to the secondorder.
 107. The method for decoding the digital motion picture accordingto claim 106, wherein step (f) further comprises the step of reselectinga frame to be outputted until the frame of the second series has beendecoded and is ready to be outputted.
 108. The method for decoding thedigital motion picture according to claim 107, wherein the frame to bereselected corresponds to the frame outputted upon receiving theinterrupt signal.
 109. The method for decoding the digital motionpicture according to claim 96, further comprising the steps of: (i)decoding the second series frames in a third order; and (ii) outputtingthe second series of frames in a fourth order different from the thirdorder.
 110. The method for decoding the digital motion picture accordingto claim 96, wherein the series of coded frames includes predictivecoded data.
 111. The method for decoding the digital motion pictureaccording to claim 96, further comprising the steps of determiningtiming of a frame to be outputted based on time information and outputorder for a frame previously outputted and output order for the frame tobe outputted.
 112. The method for decoding the digital motion pictureaccording to claim 111, wherein the output order for the framepreviously outputted and output order for the frame to be outputted eachcorrespond a display order for the respective frame.
 113. The method fordecoding the digital motion picture according to claim 96, furthercomprising the steps of: (i) extracting output order and timeinformation; and (ii) outputting the frames according to the extractedoutput order and time information.
 114. The method for decoding thedigital motion picture according to claim 113, further comprising thesteps of: (iii) obtaining reference picture data; and (iv) decoding theframes using the reference picture data.
 115. The method for decodingthe digital motion picture according to claim 106, further comprisingthe steps of: (iii) outputting the decoded frames; and (iv) storing thedecoded in predetermined locations of a memory according to an addresssignal.
 116. The method for decoding the digital motion pictureaccording to claim 96, wherein the series is coded by an MPEG codingscheme.
 117. The method for decoding the digital motion pictureaccording to claim 116, wherein said MPEG coding scheme is MPEG 2 codingscheme.
 118. The method for decoding the digital motion pictureaccording to claim 117, wherein the signal interrupting step (c)corresponds to a manually inputted signal received from an externaldevice.
 119. A digital motion picture decoding method comprising thesteps of: decoding a coded data stream as a reproduction picture;receiving a manually inputted signal which causes only one discontinuityin time sequence of a coded data stream to be decoded; rendering decodeddata, including decoded data which has not been displayed, correspondingto coded data read prior to the occurrence of the discontinuity as nulldata; and continuing to display a frame data read prior to theoccurrence of the discontinuity until a frame from coded data read afterthe discontinuity lapses is decoded and ready to be displayed.
 120. Adigital motion picture decoding method comprising the steps of: decodinga coded data stream as a reproduction picture; receiving a manuallyinputted signal which causes only one discontinuity in time sequence ofa coded data stream to be decoded; rendering decoded data, includingdecoded data which has not been displayed, corresponding to coded dataread prior to the occurrence of the discontinuity as null data; andcontinuing to display a frame displayed upon receipt of the manuallyinputted signal until a frame from coded data read after thediscontinuity lapses is decoded and ready to be displayed.
 121. Adigital motion picture decoding method as defined in claim 119, whereinsaid step of rendering decoded data as null data is for making codeddata obtained after the occurrence of the discontinuity be able to bedecoded.
 122. A digital motion picture decoding method as defined inclaim 120, wherein said step of rendering decoded data as null data isfor making coded data obtained after the occurrence of the discontinuitybe able to be decoded.